Propeller cuff



United States Patents() l` 2,729,297 PROPELLER CUFF Adolph E. FeltMilwaulsee, Wis., 'assignor to A. 0. Smith Corporation, Milwaukee, Wiss., al corporation of New York Application August 1, 1951, Serial No. 239;699=

3 Claims. (Cl, 17'0"'1^59,)

This invention relates to propeller blades and more particularly to a new and improved sh'ankf'airing or 'culi' for the same. Y

An object of the presen'tvinventiosn is to provide a light,- weight and structurally simple fairng'or cuil 'which may be conveniently attached lo' 'the 'propeller blade Without any 'projecting joints or connections 'whichz would ad# versely affect the aerodynamic 'properties of the blade.

Another object is to provide anV improved propeller blade culi which may be conveniently formed of two separate hollow members which areI independently mounted on the blade andspaced therefrom, and from each other, by an intermediate plastic-like substance.

Still another object is to provide: aflexibleculf' for a propeller blade which may be confor-med to lit varying airfoil contours caused by irregularities in construction of basically similar blades.

A further object is ltoprovide a culffor a propeller blade which willl not materially increase the. thickness ofthe bladeand result. in a. loss of aerodynarnicproperties.`

An airplane blade generally is comprised of a circular shank which. gradually flares: into the iatter air'foil shape of theblade. The shank, being constructedzwit-h this cir.- cular, non-streamlined form, provides. adequate strength for the blade and facilitates mounting thereof,4 but does not create a. stream of air adjacent. the hub portion' of the propeller. during rotationof theblade.

It has been found that the efliciencyE of the blade can be materially increased and, Where'y the propeller driving engine has cooling surfaces in. thewake of the propeller, the cooling of the engine mayl be greatly improved bypro'- viding the unstreamlined shank portion o the blade with an` airfoil fairing or cuit to create an. air stream. in the areaV sur-rounding the axis of` rotation.,v

The present invention is` directedto. a. propeller cuit for use with a propeller blade of 4airloil.-sft-ecvtioil'i. The cuir. comprises a pair of hollowairfol-shaped lighbweight metal halves or members which4 `are integrally, formed and independently mounted inchordwise. spaced. relation on the respective. leading.` and. trailing portions; of the shank of thel blade to complement the airfoilr contour y'of the blade. The cuit servesas` fa. fanl to create `arr ai-r stream adjacent the axis of rotation of the 'propeller and to direct this stream over the engine.

A resilient plastic; material, such as rubben, is disposed between the blade and the adjacent surfacestofthe vspaced cuir` halves. By vulcanizing this `intermediate rubber-layer the cuir halves are effectivelybonded; to the.` fbla'de to provide a lightweightairfoil cuilwithlnozfprojectingjoints or attachments oni the airioil surfaces; v

Figure l is a topplan view of the shank of. apropeller blade showing the cuff of the invention and with parts roken away and sectioned;

Fig. 2 is a section taken on line 2-2 of Figure l;

Fig. 3 is a section taken on line -3-3 of Figure l;

Fig. 4 is a sectio'n taken on line 4 4 of Figure l;

Fig. 5 is a section taken on Vline S-e-'S of Fig. l; and

Fig. 6 is a: detail section on the line;626 oli Fig..

Referring to thedrawings, ,there is; shown alightweight iiexible propeller cu or. taining; f1v carried on. Ithe.rshank portioni 2 of a propeller Vblade vto .provide the with an airfoil contour complementary to the airfoil contour of the blade.

Cuit 1 comprises a pair of airfoil-shaped hollow members.. or halves, oneof which is a trailing edge member 3 and the other, a leading edge member 4:

CuliC` members 3 and 4 are spaced fromveach other in 'chordwise relation on the periphery of the blade and are independently mounted on the respective trailingsand .leadl` ling edge portions of the shank of the blade with which they correspond.

The trailing edge and the leading edge ofthe respective cul members 3 and 4 are in alignment with the respective leading and trailing edges of the blade and both the trailing andleading edges of members f3 a'nd 4Vmay be swept back in the direction of the trailing edge ofthe blade to provide clearance for movement of the blade dur- -in'gpitch control.

As cuff 'members 3 and` 4 of the present invention 'are off substantially similar structure and are similarly at tached to the respective trailing edge portion and leading edge portion of the blade, the following descriptionis directed to the structure and attachmentV of only they trailing edge member 3.

Cun'- member 3 comprises a lightweight alloy sheath Shaving a generally V-shaped cross section which is integrally formed from a single sheet of` metal. Sheath 5 includes a ca-mber airfoil surface 6 and a face airfoil su'r- 'face 7 which are designed to complement the airfoil contour of the blade.

The generally curved inner edges 8 andV 9 respectively offtiie camber airfoil 6 and the face airfoil 7 of sheath 5 are substantially tangent to the respective `camber surface I0' and face surface 11 of the shank V2Y and are spaced thereon outwardly in a cliordwise direction from the longitudinal center line of said surfaces 10 and' 11.

The out-board edge 12 of the sheath is aligned with the portion of the peripheral welded joint '13' adjacent the trailing edge of the blade. Welded joint 13 serves to secure shank 2 to the central portion of the blade and extends `completely aroundV the blade.

The inboard end of sheath 5 of cut member 3 is closed by la generally triangular closure plate 14 having a base formed complementary to shank 2. Closure plate 144 is preferably constructed of lightweight sheet alloy material; and is provided with a flange 1,5 which extends substantially around the ent-ire perimeter of' plate 1'4 inboardly toward the propeller hub.

Flange 15 is in contacting relation with the inner surface yof the respective camber airfoil 6 and face airfoil 7 ofsheath 5 and is secured thereto byy stitch weld 1'6. The base portion of flange .15 of closure plate 14 complements shank 2- and is adapted to Iit within a circumferential groove, 157 formed in the annular split ring 18 which encircles shank 2. Flange 15 is secured to ring 18 by lsuitable stitch welds.

l At the base end of each side portion of flange 15 a short section of the liange is omitted for insertion of the ring 18y and thei assemblyl is clamped to ,the shank by a `split retaining ring j19 which encircles the ring 18 'on shank 2 and is adapted to tit over the curved base portion of flange 15.

Split retaining ring 19 is tightened around shank 2, by 4a clamping screw 2i), thereby securing the c losure plate 14 to the shank. An annular seal C21" encircles shan'k`j2 and is 'disposed beneath the ring l1,81. SealY v21 is compressed between the ring 18 and the shank when the split 'ring 19 is tightened.

A snap button 22 is inserted in a suitable openingV in the web of closure plate 14 to permit access-to ythe hollow. interior of cuit member 3 for removal of foreign rmatter. or for the installation. of electrical de-'icingsystems therein. t

A yokev supportH 23 4is disposed within the cui' member 3 and extends between the face airfo'il 7 and camber airfoil 6 of sheath 5. The support 23 is spaced outwardly from the inboard closure member 24 and is cushioned therefrom by rubber yoke pad 25. The support 23 prevents the airfoils 6 and 7 from spreading apart during rotation of the blade.

To provide a flexible means of attaching cuff members 3 to the shank of the blade and to prevent metal-to-metal contact between the cuff and the blade, a plurality of rubber or resilient plastic seals are interposed between the adjacent cuff and blade surfaces.

An outboard peripheral seal 26 overlaps the peripheral weld seam 13 and extends completely around the blade. Seal 26 serves to prevent metal-to-metal contact between the outboard edge 12 of sheath 5 and the underlayng shank 2.

The outboard portion of sheath partially overlaps seal 26 and the outboard edge 12 of the sheath abuts against a peripheral shoulder 27 formed in the outer surface of seal 26. The outboard portion of seal 26 tapers inwardly toward the blade to provide a smooth streamlined junction with the blade surface.

The portions of the outboard peripheral seal 26 overlapping the trailing and leading edges of the blade may be formed with an exterior slit 28 and a connecting, transversely extending, drainhole 29. Slit 28 and drainhole 29 provide a through passage between the interior of the hollow cuff member 3 and the atmosphere and serve as a drain for condensation and foreign matter which may accumulate within cuff member 3.

A camber seal 30 and a face seal 31, which are constructed of rubber or a plastic material, extend longitudinally along the respective camber surface and face surface 11 of shank 2 and serve to prevent metal-tometal contact between surfaces 10 and 11 and the respective tangential curved inner edges 8 and 9 of sheath 5.

The inboard extremities of both seals 30 and 31 abut against the annular seal 21, and the outboard extremities of seals 30 and 31 abut against the peripheral shoulder 27 of outboard seal 26.

The inner portions of face airfoil 7 and camber airfoil 6 of sheath 5 partially overlap the respective seals 30 and 3l, and the generally curved inner edges 8 and 9 of the sheath abut against a complementary curved shoulder formed in the outer surface of each of the seals 30 and 31 to provide a clean unobstructed joint on both the camber and face surfaces of the blade.

The camber seal 30 and the face seal 31 may each be formed integrally or in a number of sections depending on convenience of manufacture. The portion of each seal 30 and 31 overlapping the longitudinal center line of the respective camber and face surfaces of the shank is formed with a minimum thickness, substantially less than the thickness of the outer portions of the seals 30 and 31 which underlap the respective sheath airfoils 6 and 7, thereby substantailly maintaining the central blade thickness at a minimum and not adversely affecting the aerodynamic properties ofthe blade.

The propeller blade, together with the cuff of the present invention, is placed in a vulcanizing oven wherein the rubber seals 21, 26, 30 and 31 are cured or vulcanized to secure the cuff to the exterior surface of the blade.

The use of vulcanized rubber seals provides a lightlweight llexible attachment of the cut to the blade. Due

to resonant vibrations set up in the blade during rotational operation, the attached culi? tends to breathe or bellow in and out. The llexible attachment of the invention permits the cuff to so breathe without danger of rupture or undue stress at the point of attachment.

In addition the cuff of the invention provides a smooth aerodynamic surface, there being no projecting joints, connections or other obstructions on the airfoil surface to adversely affect the aerodynamic properties of the blade.

.Various embodiments of the invention may be employed within the scope of the following claims.

Iclaim:

l. In combination with a propeller blade of airfoil section, a cuff carried by said blade and comprising a pair of hollow cuff members mounted on the shank of the blade to complement the airfoil contour of said blade, each of said members being formed of a face surface and a camber surface joined together at their outward edges with the inner edges of the face and camber surfaces of each member disposed astride the shank and disposed generally tangentially to the face and camber surfaces of the shank, and with the inner edges of the face and camber surfaces of each member spaced in a chordwise direction from the longitudinal center line of the corresponding face and camber surfaces of the shank, each member having an open end portion facing inboardly of said blade, a closure for the open end portion of each member, reinforcing means disposed within each member and connecting the face and camber surfaces of said member to prevent said surfaces from spreading apart during rotational service of the blade, and bonding means for flexibly securing said members to the shank of said blade with said members being out of contact with said shank.

2. In combination with a propeller blade of airfoil section, a light-weight metal cuff carried by the shank of the blade to complement the airfoil contour of said blade and comprising a trailing edge member and a leading edge member, each of said members having a generally U-shaped cross section and formed with a face surface and a camber surface, said members being mounted on the shank with the face surface and camber surface of each member disposed astride said shank in a generally tangential relation to the corresponding camber and face surfaces of the shank and with the inner edges of the face and camber surfaces of each member spaced in a chordwise direction from the longitudinal center line of the corresponding camber and face surfaces of the shank, and a plastic material interposed between said members and the adjacent surface of the shank to prevent contact between said members and said shank surface and to bond the members to said blade surfaces.

3. In combination with a propeller blade of airfoil section, a light-weight metal cuff carried by the shank of the blade to complement the airfoil contour of the blade and comprising a pair of hollow cuff members, each of said members being formed of a face surface and a camber surface integrally joined at their outward edges with the inner edges of the face and camber surfaces of each member straddling the shank and disposed generally tangentially to the face and camber surfaces of the blade respectively and having the inner edges of the face and camber surfaces of one of said members spaced in a chordwise direction from the corresponding inner edges of the face and camber surfaces of the other member, a band of resilient material interposed between the outboard ends of said members and said blade, a second band of resilient material interposed between the inboard ends of said members and the shank of said blades, and a pair of resilient strips extending between said resililent bands along the face and camber surfaces of said shank and interposed between the inner edges of the face and camber surfaces of said members and said blade, said resilient material serving to flexibly bond the members to said blade.

References Cited in the file of this patent UNITED STATES PATENTS 2,309,466 Martin Jan. 26, 1943 2,427,166 Teeter Sept. 9, 1947 2,440,115 Palmatier Apr. 20, 1948 2,498,072 Dean Feb. 21, 1950 FOREIGN PATENTS 365,300 Great Britain Jan. 21, 1932 

